The present invention generally relates to diffraction gratings, particularly electro-convective diffractive devices. The present invention also relates to a method for fabricating such diffraction gratings through spontaneous self-assembly of liquid crystals into arrays of convective rolls.
Adaptive electro-optic devices are of paramount importance for information collection from the environment. In military applications, this involves both detection and evasion of weapons platforms. Because detection technologies now exploit ever-larger regions of the electromagnetic spectrum, evasion technologies must keep pace, and wavelength-agile devices that operate in the sub-millimeter infrared band are of burgeoning importance. Furthermore, there are many civilian applications for advanced diffraction gratings. Such applications include multi-spectral imaging for environmental remote-sensing, wavelength division multiplexing for communications, and spectroscopy.
Diffraction gratings are integral parts of an enormous variety of devices that employ electromagnetic radiation. A diffraction grating is realized when a material possesses a spatially periodic modulation of either the real or imaginary parts of the refractive index. When an electromagnetic wave encounters this material, the spatial modulation couples with the wavelength of the electromagnetic wave to deflect the wave in a manner depending upon its wavelength. Thus, the spatial modulation and, more specifically, the periodicity of the modulation, as well as the wavelength of the electromagnetic wave, determine the path of the electromagnetic wave through this material. This property makes gratings useful for separating multi-wavelength electromagnetic waves into their constituent wavelengths. Additionally, these diffractions gratings are useful for steering light beams by deflecting them.
The most common method for making diffraction gratings is the replica technique, in which a regular pattern of lines is scribed on a molding surface. This molding surface is then applied to a blank, usually of plastic, and the pattern is replicated on the plastic surface. Gratings like this are inexpensive and durable, but cannot be changed in any fashion after they are made. Other technologies employing chiral liquid crystals have also been used. A notable example is U.S. Pat. No. 6,188,462, wherein the spatial periodicity needed to form a grating derives from the intrinsic molecular properties of cholesteric liquid crystals. The spatial periodicity can be adjusted somewhat by applying an electric field, but the capability for more substantial adjustment in diffraction gratings is still desired in the art.
The present invention provides a dynamic method for spontaneous self-assembly of diffraction gratings. The grating spacing (also called the grating constant) and structure factor of the diffraction gratings can be tuned by the amplitude and frequency of an applied electric field.